The overall objective of this project is to characterize cutaneous and skeletal muscle vascular responses to whole-body hypothermia. In addition, the mechanisms involved in these responses are being examined by physiologically and pharmacologically dissecting the neural, humoral, viscous and direct effects of lowered body temperature. During the current year we have described and quantified the effects of hypothermia on segmental vascular resistance and transvascular fluid partitioning in skin and muscle circulations of the dog forelimb. Resistance to blood flow in all forelimb vascular segments increased when internal body temperature was reduced and this response was shown to result both from increased blood viscosity and also form active vascular smooth muscle cell contraction. Contrary to previous reports by other investigators, we did not observe active vasodilation in the muscle vasculature at anytime during cooling or hypothermia.